This invention relates a transfer for a four-wheel drive vehicle and, more particularly, to a planetary-gear-type transfer for a four-wheel drive vehicle.
FIG. 6 is a diagram of a gear train in a transfer for a four-wheel drive vehicle according to the prior art. This transfer includes a first planetary gear mechanism 60, i.e., an auxiliary speed-change unit, for exerting a speed-reducing effect, and a second planetary gear mechanism 61, i.e., a center differential, for implementing a center differential function.
In the course of investigations toward the present invention the following problem has been encountered in the art.
With the conventional transfer of the kind described above, the two functions required by the transfer (namely the speed-reducing function and center differential function) are implemented by two planetary gear mechanisms. The result is a complicated structure as well as an increase in the weight and cost of the transfer.
Accordingly, an object of the present invention is to provide a transfer, the structure of which is simplified, for a four-wheel drive vehicle.
According to an aspect of the present invention, there is provided a transfer for a four-wheel drive vehicle, comprising: an input shaft; a first output shaft disposed coaxially with respect to the input shaft; a ring gear which co-rotates with the input shaft; a first pinion meshed with the ring gear; a second pinion in mesh with the first pinion at all times; a carrier, which co-rotates with the first output shaft, for axially supporting the first and second pinions; a sun gear, which is shifted axially of the first output shaft, for being selectively meshed with the first pinion or second pinion; a locking/unlocking means for locking the sun gear against movement; and a second output shaft, which is disposed in parallel with the first output shaft, for selectively transferring torque from the first output shaft or sun gear.
According to a second aspect, there is provided a driving gear disposed on the first output shaft rotatably in unison with or relative to the first output shaft, and the transfer may be provided with synchronizing means for causing a driving gear to co-rotate with the sun gear or the first output shaft to co-rotate.
According to a third aspect, there is provided
a transfer for a four-wheel drive vehicle, comprising:
an input shaft;
a first output shaft disposed coaxially with respect to the input shaft;
a ring gear which co-rotates with the input shaft;
a first pinion meshed with the ring gear;
a second pinion in mesh with the first pinion at all times;
a carrier rotatably supporting the first and second pinions;
a sun gear, which extends axially of the first output shaft, for having one end thereof selectively meshed with the first pinion or the second pinion by the sun gear being slid axially of the first output shaft in response to an applied operation;
a brake capable of locking a second end of the sun gear when the first end of the sun gear is at a position where it will mesh with the first pinion;
a driving gear for meshing with the second end of the sun gear when the first end of the sun gear is at a position where it will mesh with the second pinion;
a sleeve mounted on the first output shaft so as to be capable of engaging with the first output shaft in a direction of rotation and of being shifted along the first output shaft axially thereof, the sleeve being shiftable so that the driving gear can be engaged with the first output shaft in the direction of rotation;
a second output shaft disposed in parallel with the first output shaft;
a driven gear, which is provided on the second output shaft so as to co-rotate therewith, for having power transmitted thereto from the driving gear.
In the transfer, when the transfer is in a high position, the sun gear is meshed with the second pinion and the driving gear, whereby torque is transmitted to the driving gear via the sun gear, and thence to the second output shaft; and
when the transfer is in a low position, the sun gear is meshed with the first pinion and is fixed by the brake, and the driving gear is engaged with the first output shaft in the direction of rotation, whereby torque is transmitted to the driving gear via the first output shaft, and thence to the second output shaft.
Further, when the transfer is in the high position, the driving gear is engaged with the first output shaft in the direction of rotation, whereby the first and second output shafts can be placed in a directly connected state.
In terms of operation of the transfer, torque is transmitted to the first output shaft via the carrier. The sun gear, on the other hand, is shifted to the other side to mesh with the second pinion so that torque is transmitted to the second output shaft via the sun gear. This establishes the high position.
Further, torque is transmitted to the first output shaft via the carrier. The sun gear, on the other hand, is shifted to one side to mesh with the first pinion and is locked by the braking means so that torque is transmitted to the second output shaft via the first output shaft. This establishes the low position.
A difference between the rotational speeds of the front and rear axles connected to the first and second output shafts, respectively, is accommodated (i.e., absorbed) by a single planetary gear mechanism comprising a ring gear, a carrier, first and second pinions and a sun gear.
Further, in accordance with the present invention, the drive gear is engaged with the first output shaft with regard to the direction of rotation, e.g., by a sleeve, even in the high position. This makes it possible to provide a transfer in which the first and second output shafts can be placed in a directly connected state.
In accordance with the transfer of the present invention as described above, both the speed-reducing and center differential functions can be implemented by a single planetary gear mechanism. In other words, the present invention provides a transfer that is simple in structure, light in weight and low in cost.
Other features and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.